Ti-Hi, BCT, and freight class: pallet math for packaging buyers

The pallet is the real unit of packaging

A retail package almost never travels alone. It gets cased, the cases get palletized, the pallets get loaded into a trailer or container. Every one of those nesting steps has a math problem attached, and the cost of getting them wrong is paid in wasted deck space, crushed product, and freight bills that run higher than the goods justify. The good news is that all of the inputs are just dimensions and weight — which means they can be computed the moment a package's geometry is known, long before a single unit is made.

Ti-Hi: how many cases fit on a pallet

Ti-Hi (also written "TiHi" or "Ti × Hi") is the shorthand for a pallet stacking pattern. It is two numbers:

• Ti — the tier count: how many cases fit in a single layer on the pallet deck.
• Hi — the high count: how many of those layers are stacked on top of each other.

Cases per pallet is simply Ti × Hi. A quick worked example on the standard 48 × 40 in pallet: the deck is 1,920 sq in. If a case footprint is 12 × 10 in, that's 120 sq in per case, and 1,920 ÷ 120 = 16 cases tile the deck with no overhang — so Ti = 16. If each case is 9 in tall and you cap the load near 45 in of product to stay trailer- and rack-friendly on top of a ~5 in pallet, you get 5 layers — so Hi = 5. That's a Ti-Hi of 16 × 5 = 80 cases per pallet.

Two real constraints shape every pattern. Overhang — cases hanging past the 48 × 40 edge lose support and shed compression strength, so keep the footprint on-deck. Gaps — cases that don't tile the deck leave voids that cut cube and make the stack less stable. The arrangement itself matters too: a column stack (cases aligned corner-to-corner up the pile) versus an interlocked or brick-laid pattern is a genuine trade-off between strength and stability, which the compression section below gets into.

The GMA pallet: the 48 × 40 standard

The default footprint across North America is the GMA pallet, named for the Grocery Manufacturers Association. It measures 48 × 40 inches, stands roughly 5–6 in tall, and weighs somewhere around 40–50 lb empty. It is one of several ISO-recognized pallet sizes, but it dominates US grocery, retail, and general freight, so pattern math, warehouse rack openings, and trailer loading are all planned around it.

Why the footprint matters to cost: a standard 53-ft dry van holds roughly 26 to 30 floor pallet positions, depending on whether pallets are loaded straight or pinwheeled. Multiply cases-per-pallet by pallets-per-trailer and you have the true landed unit count of a shipment — the denominator under your freight cost per unit. Other footprints exist (the 48 × 48 drum pallet, the 42 × 42, the EUR 1200 × 800 mm block pallet), but if nobody has specified one, assume 48 × 40.

Box compression and the McKee estimate

When pallets stack in a warehouse or nest into a trailer, the boxes at the bottom carry everything above them. Box compression test (BCT) is the measured top-to-bottom force — reported in pounds-force (lbf) — that a case withstands before it buckles, run on a platen compression tester.

You can estimate BCT before a box even exists using the McKee formula, an empirical relationship published in 1963. A commonly cited short form is:

BCT ≈ 5.87 × ECT × √(caliper × perimeter)

where ECT is the board's edge crush test (lb/in), caliper is board thickness (in), and perimeter is 2 × (length + width) of the box (in). The exact constant varies by source, so don't over-read it — the value of the formula is the shape of the relationship: stronger board, thicker board, and a larger perimeter all raise compression strength.

Treat any McKee number as an estimate, not a spec, because real cases in the real world lose strength to a stack of derates:

• Humidity. Corrugated is hygroscopic. At around 90% relative humidity, a box may retain only about half the strength it showed at standard 50% RH lab conditions. The number is approximate, but the direction is not — damp boxes are weak boxes.
• Stacking pattern. A column stack routes load straight down the strong vertical corners. Interlocking the layers buys stability against toppling but can give up a large share — often cited as roughly a third to a half — of compression strength.
• Time (creep). A box that survives a load for a minute on a tester can fail under the same load held for weeks. Long-term stacking strength is a fraction of the short-term BCT.
• Everything else. Overhang, rough handling, die-cut windows, and vent holes all subtract as well.

Because of all this, engineers design to a safety factor: the rated BCT is set well above the actual static load the bottom box must carry — multiples of 3 × or more are common — so the estimate never has to be exactly right for the stack to stay standing.

Cube utilization: don't ship air

Cube utilization is the share of available volume actually filled by product rather than void, and it applies at three levels: product-in-case, case-on-pallet, and pallet-in-trailer. Air is expensive because a load stops when it hits either its weight ceiling or its volume ceiling — it "weighs out" or "cubes out," whichever comes first. Light, bulky goods cube out (the trailer is full while far under its payload limit); dense goods weigh out (the trailer hits its weight limit with room to spare).

Right-sizing the case to the product, and the pallet pattern to the case, shrinks the void, cuts dunnage, and raises cases-per-trailer — usually the single biggest lever on freight cost per unit. A 53-ft dry van offers roughly 3,800 cu ft of usable space and a payload ceiling in the neighborhood of 45,000 lb; every cubic foot of air is capacity you paid for and didn't use.

NMFC freight class and density

For LTL (less-than-truckload) shipments, US carriers price by the NMFC — the National Motor Freight Classification, maintained by the NMFTA. It sorts commodities into 18 classes from 50 (dense, cheap to ship) to 500 (light, bulky, expensive) using four factors: density, stowability, handling, and liability. For most packaged consumer goods, density — weight per cubic foot — is the dominant one.

The Commodity Classification Standards Board publishes a density guideline that maps density to class. This is the standard published guideline and a useful planning estimate — but treat it as exactly that: some commodities carry a fixed NMFC class regardless of density, while others are explicitly density-based.

Density (lb per cubic foot)	Freight class
Less than 1	500
1–2	400
2–3	300
3–4	250
4–5	200
5–6	175
6–7	150
7–8	125
8–9	110
9–10.5	100
10.5–12	92.5
12–13.5	85
13.5–15	77.5
15–22.5	70
22.5–30	65
30–35	60
35–50	55
50 or greater	50

Each band runs from its lower number up to (but not including) the next, and the table is the published density guideline — not a guarantee. Two honest caveats: your actual class depends on the NMFC item for your specific commodity, and getting the class wrong invites a carrier reweigh-and-reclass, which is where surprise charges come from. Compute your density (total shipment weight ÷ total cubic feet, pallet included) before you book.

Dimensional weight: billed on the bigger number

Parcel carriers, and increasingly some LTL, don't just weigh your box — they price the space it occupies. Dimensional (volumetric) weight converts size into a weight:

dim weight = (L × W × H) ÷ DIM divisor

The divisor is a cubic-inches-per-pound figure set by the carrier and service — 139 is common for major US domestic parcel, with 166 also in use, and the number is often negotiable in a contract. A larger divisor means a smaller size penalty. You are billed on the billable weight, which is:

billable weight = max(actual weight, dimensional weight)

Worked example: a 20 × 16 × 12 in box is 3,840 cu in. At a divisor of 139, the dim weight is 3,840 ÷ 139 ≈ 28 lb. If the product inside actually weighs 10 lb, you still pay for 28 lb — you're shipping 18 lb of air. Shrink the box to the product and the billable weight falls back toward the real weight. It is the parcel-scale version of the same lesson as cube utilization: void costs money.

How PackOS turns geometry into a shippable unit

Every number above is a function of dimensions and weight — which is exactly what PackOS already holds once it has rebuilt a package into an editable parametric model. From the finished case size and weight it computes the Ti-Hi against a chosen pallet (defaulting to the GMA 48 × 40), the resulting cases per pallet, load height, and pallet weight; it flags overhang; it estimates compression headroom against the stack; it derives a freight class from density; and it compares actual against dimensional weight — so a dieline becomes a costed, shippable unit, not just a shape. You can see the packout and freight logic on the technology page, or run it on a real file with Quick Quote.